adventitious

adj. happening by chance; not inherent; occurring accidentally

Adventitious, in botany, refers to structures that develop in an unusual place, and in medicine, it refers to conditions acquired after birth. This article discusses adventitious roots, buds and shoots, that are very common in vascular plants.
See more at Wikipedia.org...

Adjective
1. associated by chance and not an integral part; "poetry is something to which words are the accidental, not by any means the essential form"- Frederick W. Robertson; "they had to decide whether his misconduct was adventitious or the result of a flaw in his character"
(synonym) accidental
(similar) extrinsic

(a.)
Out of the proper or usual place; as, adventitious buds or roots.
  

(a.)
Added extrinsically; not essentially inherent; accidental or causal; additional; supervenient; foreign.
  

(a.)
Acquired, as diseases; accidental.
  

(a.)
Accidentally or sparingly spontaneous in a country or district; not fully naturalized; adventive; -- applied to foreign plants.
  

adjective
which is on the outside
adventitious bursa = see BURSA